Considering the Haskell code:

do  -- it's IO !!!
  ...
  !x <- someFunction
  ... usage of x

how useful is ! here? It’s a result of monadic (it’s IO !) evaluation, so my questions are:

1. if x is a primitive type like UTCTime (getCurrentTime for example), Int, Bool – does ! make sense?

2. if x has “head” like String, Map k v, some record maybe? Then x can be lazy? How lazy? Does it mean that when I will use x later then real IO happens?

3. Does IO monad have some more specific behavior in this context? Like little bit more strict than other (more “pure”) monads?

By default I/O is lazy, then how does Haskell know when to call it immediately (passing through this expression) or when to substitute it with a thunk? By type of x? Something like: GHC has a list of primitive types and everything outside the list is substituted?

Any explanations are appreciated.